keyboardWillShowNotification called twice when dismissed

Question

I've subscribed to keyboardWillShowNotification and keyboardWillHideNotification to move around my UI. I've noticed that when I dismiss the keyboard by tapping the "Go" button, keyboardWillShowNotification is called twice (thus reseting some of my constraints) however if dismiss by hitting return on the keyboard (MacBook) then it's not called twice.

How can I avoid it being called twice? Why is this behaviour even there? I can't find any mention of it (lots of references to it being called twice with input views...etc) but never when being dismissed.

Here's my code:

override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardNotification(notification:)), name: UIResponder.keyboardWillShowNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWasDismissed(notification:)), name: UIResponder.keyboardWillHideNotification, object: nil) 
}

and...

@objc func keyboardNotification(notification: NSNotification) {
        guard
            let animationDuration = notification.userInfo?["UIKeyboardAnimationDurationUserInfoKey"] as? Double,
            let animationCurve = notification.userInfo?["UIKeyboardAnimationCurveUserInfoKey"] as? NSNumber,
            let frameEnd = notification.userInfo?["UIKeyboardFrameEndUserInfoKey"] as? CGRect,
            let frameBegin = notification.userInfo?["UIKeyboardFrameBeginUserInfoKey"]
            else {
                print("No userInfo recived from NSNotification.Name.UIKeyboardWillShow")
                return
        }
        print("WILL SHOW")

        let margin = self.view.safeAreaLayoutGuide
        constraintsWhenKeyboardVisible = [
                            boxOffice.leadingAnchor.constraint(equalTo: margin.leadingAnchor),
                            boxOffice.trailingAnchor.constraint(equalTo: margin.trailingAnchor),
                            boxOffice.bottomAnchor.constraint(equalTo: margin.bottomAnchor),
                            boxOffice.topAnchor.constraint(equalTo: self.view.bottomAnchor, constant: -(frameEnd.height + 50))
                        ]
        NSLayoutConstraint.deactivate(boxOfficeFinalConstraints)
        NSLayoutConstraint.activate(constraintsWhenKeyboardVisible)

        UIView.animate(withDuration: animationDuration,
                       delay: TimeInterval(0),
                       options: UIView.AnimationOptions(rawValue: animationCurve.uintValue),
                       animations: {
                        self.boxOffice.answerField.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
                        self.view.layoutIfNeeded()
        },
                       completion: nil)
    }


@objc func keyboardWasDismissed(notification: NSNotification) {
        guard
            let animationDuration = notification.userInfo?["UIKeyboardAnimationDurationUserInfoKey"] as? Double,
            let animationCurve = notification.userInfo?["UIKeyboardAnimationCurveUserInfoKey"] as? NSNumber
            else {
                print("No userInfo recived from NSNotification.Name.UIKeyboardWillShow")
                return
        }
        print("WILL HIDE")
        //print(notification)
        NSLayoutConstraint.deactivate(self.constraintsWhenKeyboardVisible)
        NSLayoutConstraint.activate(self.boxOfficeFinalConstraints)

        UIView.animate(withDuration: animationDuration,
                       delay: TimeInterval(0),
                       options: UIView.AnimationOptions(rawValue: animationCurve.uintValue),
                       animations: {
                        self.boxOffice.answerField.layer.maskedCorners = [.layerMaxXMaxYCorner, .layerMaxXMinYCorner, .layerMinXMaxYCorner, .layerMinXMinYCorner]
                        self.view.layoutIfNeeded()
        },
                       completion: nil)

    }

Answer 1

I haven't solved the issue of keyboardWillShowNotification being posted when Return is hit on the iOS keyboard simulator but not on the hardware keyboard in the simulator, but I have modified my code so that when the keyboard is shown I don't add constraints, I simply modify the constant of the constraint using the height from the keyboard notification. This has solved it.

boxOfficeWhenKeyboardVisible[3].constant = -(frameEnd.height + 50)